sql作业

基础完成

1、查询男生、女生的人数；
select gender,count(gender) as gender_num from student group by gender;
2、查询姓“张”的学生名单；
select sname from student where sname regexp '^张';
select sname from student where sname regexp '张{1}';
select sname from student where sname like '张%';
3、课程平均分从高到低显示
select course.cname,avg(score.num) as avg_num from score inner join course where score.course_id = course.cid group by cname order by avg_num desc;
4、查询有课程成绩小于60分的同学的学号、姓名；
select distinct student.sid,student.sname from score inner join student on score.student_id = student.sid  where score.num < 60;
5、查询至少有一门课与学号为1的同学所学课程相同的同学的学号和姓名；
SELECT DISTINCT
    student.sid,
    student.sname
FROM
    score
    INNER JOIN student ON score.student_id = student.sid
WHERE
    course_id IN ( SELECT course_id FROM score WHERE student_id = 1 );
6、查询出只选修了一门课程的全部学生的学号和姓名；
select sid,sname from student inner join (select student_id,course_id from score group by student_id having count(score.course_id) = 1) as s_sid on student.sid = s_sid.student_id;
7、查询各科成绩最高和最低的分：以如下形式显示：课程ID，最高分，最低分；
select course_id as '课程ID',max(num) as '最高分' ,min(num) as '最低分' from score  group by course_id;
select course_id as '课程ID',max(num) as '最高分' ,min(num) as '最低分' from score  where score.course_id in (select cid FROM course) group by course_id;
select course_id as '课程ID',max(num) as '最高分' ,min(num) as '最低分' from score  group by course_id  having score.course_id in (select cid FROM course);
select concat_ws(',',course_id,max(num),min(num)) as fp from score  group by course_id  having score.course_id in (select cid FROM course);
select concat('课程ID: ',course_id,' 最高分：',max(num),' 最低分：',min(num)) as fp from score  group by course_id  having score.course_id in (select cid FROM course);
8、查询课程编号“2”的成绩比课程编号“1”课程低的所有同学的学号、姓名；
SELECT
    sid,
    sname
FROM
    student
    INNER JOIN (
SELECT
    st_id1,
    sc1,
    sc2
FROM
    ( SELECT student_id AS st_id1, num AS sc1 FROM score WHERE course_id = 1 ) AS num_1,
    ( SELECT student_id AS st_id2, num AS sc2 FROM score WHERE course_id = 2 ) AS num_2
WHERE
    st_id1 = st_id2
    AND sc2 < sc1
    ) AS sr ON student.sid = sr.st_id1;
9、查询“生物”课程比“物理”课程成绩高的所有学生的学号；
SELECT
    sid
FROM
    student
    INNER JOIN (
SELECT
    stu_swid,
    sw_num,
    wl_num
FROM
    (
SELECT
    student_id AS stu_swid,
    num AS sw_num
FROM
    score
WHERE
    score.course_id = ( SELECT cid AS sw_cid FROM course WHERE cname = '生物' )
    ) AS sw,
    (
SELECT
    student_id AS stu_wlid,
    num AS wl_num
FROM
    score
WHERE
    score.course_id = ( SELECT cid AS sw_cid FROM course WHERE cname = '物理' )
    ) AS wl
WHERE
    stu_swid = stu_wlid
    AND sw_num > wl_num
    ) AS super ON student.sid = super.stu_swid;
10、查询平均成绩大于60分的同学的学号和平均成绩;
SELECT
    sid,
    convert(avg_me.avg_num,decimal(5,2)) as avg_num
FROM
    student
    INNER JOIN ( SELECT student_id, avg( num ) AS avg_num FROM score GROUP BY student_id HAVING avg_num > 60 ) AS avg_me ON student.sid = avg_me.student_id;
11、查询所有同学的学号、姓名、选课数、总成绩；
SELECT
    student.sid,
    student.sname,
    count( score.course_id ) AS count_course,
    sum( num ) AS num_score
FROM
    student
    LEFT JOIN score ON student.sid = score.student_id
GROUP BY
    student.sid
12、查询姓“李”的老师的个数；
select count(tid) as count_tid from teacher where tname  regexp '^李';
select count(tid) as count_tid from teacher where tname  regexp '李.*';
select count(tid) as count_tid from teacher where tname  like '李%';
13、查询没学过“张磊老师”课的同学的学号、姓名；
SELECT
    sid,
    sname
FROM
    student
WHERE
    sid NOT IN (
SELECT
    student_id
FROM
    score
WHERE
    course_id = ( SELECT cid FROM course INNER JOIN teacher ON course.teacher_id = teacher.tid WHERE tname = '张磊老师' )
    );
14、查询学过“1”并且也学过编号“2”课程的同学的学号、姓名；
SELECT
    sid,
    sname
FROM
    student
WHERE
    sid IN (
SELECT
    cor1.student_id
FROM
    (
    ( SELECT student_id, course_id AS cid_1 FROM score WHERE course_id = 1 ) AS cor1,
    ( SELECT student_id, course_id AS cid_2 FROM score WHERE course_id = 2 ) AS cor2
    )
WHERE
    cor1.student_id = cor2.student_id
    )
15、查询学过“李平老师”所教的所有课的同学的学号、姓名；
SELECT
    sid,sname
FROM
    student,
    (
SELECT
    student_id,
    group_concat( course_id ORDER BY course_id ASC ) AS grp_co
FROM
    score
    INNER JOIN ( SELECT cid FROM course INNER JOIN teacher ON course.teacher_id = teacher.tid WHERE tname = '李平老师' ) AS s1 ON course_id = cid
GROUP BY
    student_id
    ) AS grp_s
WHERE
    student.sid = grp_s.student_id
    AND grp_co = ( SELECT GROUP_CONCAT( cid ) FROM course INNER JOIN teacher ON course.teacher_id = teacher.tid WHERE tname = '李平老师' );

进阶完成

1、查询没有学全所有课的同学的学号、姓名；
# 方法一
select student_id,sname from score inner join student on score.student_id = student.sid group by student.sid having count(course_id) < (select count(cid) from course)
# 方法二
SELECT
    sid,
    sname
FROM
    student
WHERE
    sid IN (
SELECT
    student_id
FROM
    ( SELECT student_id, GROUP_CONCAT( course_id ) AS stu_id FROM score GROUP BY student_id ) AS stu_con,
    ( SELECT GROUP_CONCAT( cid ORDER BY cid ASC ) AS cor_id FROM course ) AS cor_con
WHERE
    stu_id != cor_id
    );
2、查询和“002”号的同学学习的课程完全相同的其他同学学号和姓名；
SELECT
    sid,
    sname
FROM
    student
WHERE
    sid = (
SELECT
    stu_con.student_id
FROM
    ( SELECT student_id, GROUP_CONCAT( course_id ORDER BY course_id ASC ) AS stu_id FROM score GROUP BY student_id ) AS stu_con,
    ( SELECT student_id, GROUP_CONCAT( course_id ORDER BY course_id ASC ) AS stu_id FROM score GROUP BY student_id HAVING student_id = 2 ) AS stu2_con
WHERE
    stu_con.stu_id = stu2_con.stu_id
    AND stu_con.student_id != stu2_con.student_id
    );
3、删除学习“叶平”老师课的SC表记录；
# 数据准备一下
insert into teacher(tname) values('叶平老师');
insert into course(cname,teacher_id) values('心理学',6);
insert into score values(53,2,5,97),(54,13,5,95);
# 删除数据
delete from score where course_id = (select cid from course inner join teacher where course.teacher_id = teacher.tid and teacher.tname = '叶平老师');
4、向SC表中插入一些记录，这些记录要求符合以下条件：①没有上过编号“002”课程的同学学号；②插入“002”号课程的平均成绩；
select sid from student where sid not in (select student_id from score where course_id = 2 );
select avg(num) from score group by course_id having course_id = 2; 
insert into score values(82,2,2,68),(83,13,2,68),(84,14,2,68),(85,15,2,68),(86,16,2,68);
5、按平均成绩从低到高显示所有学生的“生物”、“物理”、“体育”三门的课程成绩，按如下形式显示： 学生ID,生物,物理,体育,有效课程数,有效平均分；
SELECT
    concat_ws(
    ' ',
    '学生id:',student.sid,
    '生物/物理/体育:',group_concat( CASE WHEN score.num IS NOT NULL THEN score.num ELSE concat( 'null' ) END ORDER BY course.cname DESC ),
    '有效课程数:',count( score.course_id ),
    '有效平均数:',CONVERT ( avg( score.num ), DECIMAL ( 5, 2 ) )
    )
FROM
    student
    INNER JOIN course ON cname IN ( '生物', '物理', '体育' )
    LEFT JOIN score ON student.sid = score.student_id
    AND course.cid = score.course_id
GROUP BY
    student.sid
ORDER BY
    avg( score.num )
6、查询各科成绩最高和最低的分：以如下形式显示：课程ID，最高分，最低分；
# 方法一
select concat_ws(',',course_id,max(num),min(num)) as fp from score  group by course_id  having score.course_id in (select cid FROM course);
# 方法二
select course_id as '课程ID',max(num) as '最高分' ,min(num) as '最低分' from score  group by course_id  having score.course_id in (select cid FROM course);
# 方法三
select concat('课程ID: ',course_id,' 最高分：',max(num),' 最低分：',min(num)) as fp from score  group by course_id  having score.course_id in (select cid FROM course);
7、按各科平均成绩从低到高和及格率的百分数从高到低顺序；
# 平均成绩从低到高排序
select score.course_id,course.cname,avg(num) as avg_num  from score inner join course on score.course_id = course.cid group by score.course_id order by avg_num asc;
# 及格率百分数从高到底排序
SELECT    course_id,    convert(sum( CASE WHEN score.num > 60 THEN 1 ELSE 0 END ) / count(1) * 100,DECIMAL(5,2)) as percent FROM    score GROUP BY course_id order by     percent desc;
8、查询各科成绩前三名的记录:(不考虑成绩并列情况)
# 方法一
SELECT  a.course_id,a.cname,SUBSTRING_INDEX(a.num, ',', 3)  as score from (SELECT GROUP_CONCAT(num ORDER BY num desc) as num ,course_id,course.cname  from score inner join course on score.course_id = course.cid GROUP BY score.course_id ) as a
# 方法二
select s1.course_id,s1.student_id,s1.num as score,count( DISTINCT s2.num) as sort_num
from score as s1
inner join score as s2
on s1.course_id = s2.course_id and s1.num <= s2.num
group by s1.course_id,s1.num having sort_num <= 3 order by s1.course_id,s1.num desc ;
9、查询每门课程被选修的学生数；
select  score.course_id,course.cname,count(score.student_id) as student_count from score inner join course on score.course_id = course.cid group by score.course_id
10、查询同名同姓学生名单，并统计同名人数；
insert into student values(17,'女',3,'刘四');
select sname,count(sname) as same_num from student group by sname having same_num > 1;
11、查询每门课程的平均成绩，结果按平均成绩升序排列，平均成绩相同时，按课程号降序排列；
select course_id,CONVERT(avg(num),decimal(5,2)) as avg_num from score group by course_id order by avg_num asc,course_id desc;  
12、查询平均成绩大于85的所有学生的学号、姓名和平均成绩；
insert into score values(81,14,5,100);
# 85分的同学原数据没有，所以手动插入一条，并且将85分条件暂时定为80
SELECT
    sid,
    sname,
    avg_num
FROM
    student
    INNER JOIN ( SELECT student_id, avg( num ) AS avg_num FROM score GROUP BY student_id HAVING avg_num > 80 ) AS avg_sid ON student.sid = avg_sid.student_id;
13、查询课程名称为“数学”，且分数低于60的学生姓名和分数；
# 没有数学用物理替代
# 方法一
select st.sname,score.num as score from score inner join course on score.course_id = course.cid and course.cname = '物理' inner join (select sid,sname from student) as st on st.sid = score.student_id where num < 60
# 方法二
SELECT
    sname,
    num AS score
FROM
    student
    INNER JOIN (
SELECT
    student_id,
    num
FROM
    score
    INNER JOIN ( SELECT cid FROM course WHERE cname = '物理' ) AS c ON course_id = c.cid
WHERE
    num < 60
    ) AS cc ON student.sid = cc.student_id;
14、查询课程编号为003且课程成绩在80分以上的学生的学号和姓名；
# 方法一
select student.sid,student.sname from score inner join student on student_id = student.sid where course_id = 3 and num > 80;
# 方法二
SELECT
    sid,
    sname
FROM
    student
    INNER JOIN (
SELECT
    student_id,
    num
FROM
    score
    INNER JOIN ( SELECT cid FROM course WHERE cid = '3' ) AS c ON course_id = c.cid
WHERE
    num > 80
    ) AS score_8 ON student.sid = score_8.student_id;
15、求选了课程的学生人数
SELECT
    count( studentd.student_id ) AS same_count_stu
FROM
    ( SELECT student_id FROM score GROUP BY student_id HAVING count( course_id ) > 0 ) AS studentd;
16、查询选修“杨艳”老师所授课程的学生中，成绩最高的学生姓名及其成绩；
SELECT
    st.sname,
    s.num
FROM
    score s
    INNER JOIN course c ON c.cid = s.course_id
    INNER JOIN teacher t ON t.tid = c.teacher_id
    INNER JOIN student st ON st.sid = s.student_id
WHERE
    t.tname = '刘海燕老师'
ORDER BY
    s.num DESC
    LIMIT 1;
17、查询各个课程及相应的选修人数；
SELECT
    cid,
    cname,
    count( student_id ) AS count_st
FROM
    course c
    INNER JOIN score s ON c.cid = s.course_id
GROUP BY
    s.course_id;
18、查询不同课程但成绩相同的学生的学号、课程号、学生成绩；
SELECT
    score.student_id,
    GROUP_CONCAT( score.course_id ) cor_id,
    score.num
FROM
    score
    INNER JOIN score c ON score.num = c.num
    AND score.course_id != c.course_id
    AND score.student_id = c.student_id
GROUP BY
    score.student_id;
19、查询每门课程成绩最好的前两名；
select SUBSTRING_INDEX(cc.st_id, ',', 2) as stid,SUBSTRING_INDEX(cc.sc, ',', 2) as sc from (select group_concat(student_id order by num desc) as st_id,group_concat(num order by num desc) as sc from score sc1 where (select count(1) from score sc2 where sc2.course_id = sc1.course_id and sc2.num > sc1.num  ) <=2 group by sc1.course_id order by sc1.course_id asc,sc1.num desc) as cc;
20、检索至少选修两门课程的学生学号；
select student_id  from score group by student_id having count(course_id) > 1;
21、查询全部学生都选修的课程的课程号和课程名；
select course.cid,course.cname from score inner join course on score.course_id = course.cid group by cid,cname having count(student_id) = (select count(sid) from student);
22、查询没学过“叶平”老师讲授的任一门课程的学生姓名；
select sname from student where sid not in (select student_id from score inner join course on score.course_id = course.cid inner join teacher on tname = '李平老师' and teacher_id = tid group by student_id);
23、查询两门以上不及格课程的同学的学号及其平均成绩；
# 方法一
select score.student_id,avg(num) avg_num from score inner join (select student_id from score where num < 60 group by student_id having count(student_id) > 1) as sm on score.student_id = sm.student_id group by score.student_id
# 方法二
select student_id,avg(num) avg_num from score where student_id in (select student_id from score where num < 60 group by student_id having count(student_id) > 1) group by score.student_id ;
24、检索“004”课程分数小于60，按分数降序排列的同学学号；
select student_id from score where course_id = 4 and num < 60 order by num desc;
25、删除“002”同学的“001”课程的成绩；
delete from score where student_id = 2 and course_id = 1;